Last Modified: Sep 30, 2026
Affected Product(s):
BIG-IP LTM
Known Affected Versions:
17.1.0, 17.1.0.1, 17.1.0.2, 17.1.0.3, 17.1.1, 17.1.1.1, 17.1.1.2, 17.1.1.3, 17.1.1.4, 17.1.2, 17.1.2.1, 17.1.2.2, 17.1.3, 17.1.3.1, 17.1.3.2, 17.1.3.4, 17.1.3.5, 17.5.0, 17.5.1, 17.5.1.2, 17.5.1.3, 17.5.1.4, 17.5.1.5, 17.5.1.6, 17.5.1.8, 17.5.1.9, 21.0.0, 21.0.0.1, 21.0.0.2, 21.0.0.3, 21.1.0, 21.1.0.1, 21.1.0.2
Opened: Sep 24, 2026 Severity: 3-Major
After a series of updates to the records provided by the configured DNS server, ephemeral nodes and pool members associated with fully qualified domain names (FQDNs) that are created temporarily during the transition may not be removed once the DNS change is complete and the FQDNs resolve back to the original set of IP addresses
Traffic may continue to be directed to IP addresses that were only provided by the DNS server for a brief period of time, after the DNS zone records revert to their original configuration
This situation may occur under the following conditions: - LTM pools are configured using Fully Qualified Domain Name (FQDN) nodes and pool members - Many of the configured FQDNs resolve to the same IP address(es) - The DNS server temporarily resolves the FQDNs to a different set of address records before reverting back to the original set of records. This can happen, for example, during maintenance on the DNS server or when a zone update is applied and then quickly undone - The time period during which the DNS server provides a different set of records is shorter than the "interval" value (DNS query interval) configured for the FQDN nodes. This condition also applies if the FQDN node is set with an "interval" value equal to the TTL (Time to Live), and the TTL returned by the DNS server is longer than the duration of the temporary record change
To work around this problem when it occurs, restart the Dynamic Configuration daemon (dynconfd) by issuing the following command at the BIG-IP console: bigstart restart dynconfd To prevent this issue from occurring, allow the temporary DNS server configuration change to persist longer than the query interval specified for the configured FQDN nodes, or the TTL interval configured in the DNS zone records if the FQDN nodes are configured with an interval of "ttl"
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